The present invention relates generally to the field of wireless communication and in particular to a system and method of mitigating RF interference experienced by an OFDM receiver in a portable electronic device from RF signals intermittently transmitted by the device.
Digital Video Broadcast-Terrestrial (DVB-T) is a well-defined standard for the broadcast of video content in digital format. DVB-T utilizes Orthogonal Frequency Domain Multiplexing (OFDM) modulation. DVB-H (Handheld) is a recent extension of the DVB-T standard that optimizes digital video transmission to portable (handheld) electronic devices, including wireless communication system mobile terminals. The DVB-H extensions include time slicing to reduce power consumption at the receiver, IP datacasting for lower-resolution video streaming, multiprotocol encapsulation-forward error correction (MPE-FEC) for more robust signal reception, and a 4K OFDM carrier mode (in addition to the 2K and 8K modes defined for DVB-T) for wireless network optimization. DVB-H can transmit MPEG-4 video streams at 11 Mbits/sec, allowing 30-35 video streams to portable devices at 150-400 kbits/sec, sufficient to render acceptable quality video resolution on small screens.
In the US, DVB-H will occupy an approximately 5-MHz segment of the L-band, which spans approximately 0.39 to 1.55 GHz. In one implementation, the upper end of the spectrum required for DVB-H is approximately 750 MHz, providing at least 75 MHz separation from the lower end of the spectrum required for the transmission of GSM bursts (825 MHz in the US; 880 MHz in Europe) in mobile terminals supporting the Global System for Mobile Communications (GSM). The periodic GSM communication signal transmission bursts (0.576 msec burst within every 4.6 msec frame) do not directly interfere with DVB-H reception. However, as well known in the art, mobile terminal transmitters exhibit frequency roll off, wherein attenuated RF energy is emitted outside of a bandpass frequency boundary, rather than the ideal complete suppression of all RF energy past the frequency boundary. Accordingly, some RF energy from GSM communication transmissions may “leak” into the DVB-H reception frequencies, causing interference.
To avoid such interference, a Surface Acoustic Wave (SAW) filter may be incorporated into the mobile terminal transceiver design, providing a sharper frequency roll off for the GSM burst transmissions. However, a SAW filter increases the transceiver design complexity, and both increases cost and reduces reliability by adding an additional component. Furthermore, the filter introduces loss and causes the GSM power amplifier to operate at a higher output power, reducing battery life. Particularly since not all mobile terminals will receive DVB-H signals, it would be advantageous to reduce or eliminate the deleterious effects of GSM burst transmissions on DVB-H signal reception, without the need for a SAW filter.